Saturable reactor control



July 9, 1957 w. SCHAELCHLIN ETAL 2,798,571

SATURABLEI REACTOR CONTROL Filed June 26, 1953 WITNESSES: INVENTORS Wol'ler Schoelchlin 8 9% choregon H. Storey,

ATTORNEY United States atent sATnnAsLE REACTOR coNrRot Walter Schaelchlin and (Jharlton H. Storey, Jr., Buffalo, N. Y., assignors to Westinghouse Electric tlorporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application June 26, 1953, Serial No. 364,364

r? Ciaims. (Cl. 183-4) This invention relates to electrical control apparatus for eliminating a system fault current and returning the system to normal voltage within a relatively short time interval. In more particular, the invention relates to a control system of the type referred to which utilizes a saturable core impedance device.

Although the invention is broadly applicable to apparatus for eliminating a system fault current and returning the system to normal voltage, it is illustrated here as applied to precipitators for removing ionized particles from a contaminated atmosphere. An example being the Cottrell type precipitator for removing particles from the exhaust stacks of industrial plants.

Precipitators of the type contemplated present a capacitive load and are subject to arc-over between elements. The control must extinguish the arc in the precipitator and return the precipitator voltage to its normal value as quickly as possible.

One object of this invention is to provide control apparatus for extinguishing or eliminating a system fault current.

Another object of this invention is to provide control apparatus for extinguishing or eliminating a system fault current and restoring normal voltage to the system after the fault current has been extinguished or eliminated.

A specific object of this invention is to provide a control system for an electrostatic precipitator wherebyany arc-over between elements is automatically eliminated and normal voltage restored to the system.

Many control systems for precipitators utilize a ballast rheostat in series with the primary of the transformer which supplies the voltage for the precipitators so as to keep the fault current at a reasonable value and to adjust the transformer voltage to a value close to the breakdown point of the precipitator in order to insure a maximum operating efficiency of precipitation. The system has a fast speed of response because there is no time delay in the ballast rheostat. However, it has a poor operating efficiency because of the loss in the rheostat, a special ventilating system is required to dissipate the heat caused by these losses, and the voltage adjustment by meansof the rheostat is'rather coarse because of the limited number of steps.

Accordingly, a further specific object of this invention is to provide a control system of the type referred to which utilizes a saturable core impedance device and has positive arc extinguishing characteristics with a relatively fast response, high efficiency, and low loss for restoring a normal voltage to the precipitator after an arcover.

The objects stated are merely illustrative. Still other objects and advantages will become apparent from a study of the following specification and the accompanying drawing. The single figure shows diagrammatically a circuit embodying the invention.

With specific reference to the form of the invention illustrated an electrostatic precipitator is designed by the numeral 1 and is shown as having a pipe 2 through which the treated material flows and a bus 3 in the center of the pipe comprising the elements which receive the direct current ionizing voltage. The relatively high direct current ionizing voltage for the electrostatic precipitator 1 is supplied from the positive and negative terminals 4 and 5 of the full-wave rectifier 6. The alternating current terminals 7 and it of the rectifier 6 are connected to the output terminals of the secondary S of the transformer 9. The primary winding P of the transformer 9 has voltage adjusting taps at one end connected to one line Ll of an alternating current supply through the voltage adjusting arm ill. The opposite side of the primary P of the transformer h is connected to the opposite line L2 of the alternating current source through series connected windings l1 and 12 of a saturable core reactor 13. The rectifier 6 is shown as the dry type rectifier but other type rectifiers which are capable of supplying the necessary ionizing voltage to the electrostatic precipitator 1 may be used.

The saturable core reactor 13 has a control winding 14 which receives a direct current voltage from the output terminals 15 and 16 of a full-wave rectifier 17. A voltage adjusting potentiometer ifi is connected in series with the control winding M. The input terminals 19 and 20 of the rectifier i7 are supplied from a magnetic amplifier 21 of the self-saturating type having main windings 22 and 23 and saturating rectifiers 24 and 25. The main windings 22 and 23 of the magnetic amplifier 21 are supplied from a variable voltage autotransformer 26 which is connected across the secondary of the transformer 27. The primary of the transformer 27 .is connected directly across the lines L1 and L2 which supply an alternating current voltage.

The magnetic amplifier 21 has a bias winding 28 connected in series with a voltage adjusting potentiometer 29 across the output terminals 39 and 31 of rectifier 32 connected in full-bridge arrangement. The input terminals 33 and 34 of the rectifiers 32 in full-bridge arrangement are also connected across the secondary of the transformer 27. In the embodiment illustrated, the bias winding 28 saturates the core of the magnetic amplifier 21. The magnitude of the voltage applied to the bias winding 28 is such that it will result in the necessary current into the control winding 14 of the saturable core reactor 13, so that the main windings 11 and 12 thereof will present the desired circuit impedance. A control winding 35 is provided for the magnetic amplifier 21 and is connected in series With a resistor 36 across the output terminals 37 and 38 of rectifiers 39 in full-bridge arrangement. The resistor 36 is introduced to reduce the time delay of the magnetic amplifier. The rectifiers 39 have their input terminals 4% and 41 connected to be supplied from the secondary of the current transformer 42 so that the control winding 35 of the magnetic amplifier 21 will receive a signal determined by the current which flows through the primary P of the transformer 9. The control winding 35 is wound on the core of the magnetic amplifier 21 in such a manner that its flux opposes that caused by the bias winding 28 and therefore the effect of the control winding 35 is to desaturate the core of the magnetic amplifier 21.

For normal operation the voltage on the bias winding 28 of the magnetic amplifier 21 is such that it tends to saturate the core of the magnetic amplifier and give a desired current in the control winding 14 of the saturable core reactor 13. The current in the control winding 14 of the saturable core reactor 13 is such that the saturable reactor is reasonably well saturated. The variable voltage autotransformer 26 is provided to permit fine adjustment of the voltage on the precipitator 1 by means of changing the voltage supply on the main windings 22 and 23 of the magnetic amplifier 21 to thus change the currents applied to the control winding 14 of saturable reactor 13 and vary saturation of its cores and hence impedance of its main windings 11 and 12. Varying the impedance presented by the main windings 11 and 12 varies the voltage on the primary P of the transformer 9 and thus the voltage applied to the elements 2 and 3 of the precipitator 1.

In case of a fault current or an arc-over between the elements 2 and 3 of the precipitator 1, a current surge will occur in the circuit of the primary P of the transformer 9 as well as in the circuit of the secondary S. The current surge in the circuit of the primary P of transformer 9 will cause an immediate and corresponding rise in the secondary output of the current transformer {12 to the control winding 35 of the magnetic amplifier 21 The control winding ampere turns then will predominate to desaturate the magnetic amplifier and thereby reduce the current of the control coil 14 of the saturable core reactor which in turn increases the impedance presented by its main windings 11 and 12. As soon as the'impedance of the main windings l1 and 12 of the saturable core reactor is increased, the voltage across the primary P of the transformer 9 is decreased to the extent that the arc in precipitator 1 is extinguished. When the arc in the precipitator 1 is extinguished the entire system current will decrease. The bias winding 28 of the magnetic amplifier 21 will again determine the degree of saturation of the core and the primary P of transformer 9 will be restored to normal and hence the voltage between the elements 2 and 3 of the precipitator 1 will be restored to normal.

It will be recognized that the objects of the invention have been achieved by providing a control apparatus utilizing saturable core impedance devices to extinguish or eliminate a system fault current and restore normal operating voltage to the system very rapidly. It will also be recognized that the system utilized has a high operating efficiency.

While in accordance with the patent statutes, one best known embodiment of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby but that equivalents are clearly within the inventive scope.

We claim as our invention:

1. Electrical control apparatus comprising the combination of a transformer having a primary and a secondary, rectifying means connected to said secondary to supply a direct current voltage, a capacitive load connected to said rectifying means to receive said direct current voltage, a first saturable core impedance device having its main windings connected between an alternating current source and the transformer primary, a control winding for said first saturable core impedance device, a second saturable core impedance device connected to energize said control winding of said first saturable core impedance device, winding circuit means for said second saturable core impedance device connected to saturate said second saturable core impedance device, and control winding means for said second saturable core impedance device responsive to transformer current and connected to desaturate said second saturable core impedance device to reduce the output thereof upon the occurrence of transformer current of a given value.

2. Electrical control apparatus comprising, the combination of a transformer having a primary and a secondary, rectifying means connected to said secondary to supply a direct current voltage, a capacitive load connected to said rectifying means to receive said direct current voltage, a first saturable core impedance device having its main windings connected between an alternating current source and the transformer primary, a control winding for said first saturable core impedance device, a second saturable core impedance device having an output circuit connected to energized said control winding of said first saturable core impedance device, a bias winding for said second saturable core impedance device, means for applying a bias voltage to said bias winding, said bias winding being wound to provide a saturating flux, a control winding for said second saturable core impedance device, and means responsive to the rate of change of transformer current for energizing said last named control winding in a sense to produce a saturating flux in said second saturable core impedance device.

3. Electrical control apparatus comprising, the combination of a transformer having a primary and a secondary, rectifying means connected to said secondary to supply a direct current voltage, a capacitive load connected to said rectifying means to receive said direct current voltage, a saturable core impedance device having its main windings connected between an alternating current source and the transformer primary, a control winding for said saturable core impedance device, a magnetic amplifier of the self-saturating type having an output circuit connected to energize said control winding of said saturable core impedance device, a bias winding circuit for said magnetic amplifier connected to bias said magnetic amplifier toward maximum output, a control winding on said magnetic amplifier disposed to drive said magnetic amplifier toward minimum output, and means responsive to transformer current for energizing said control winding of said magnetic amplifier.

4. Electrical control apparatus comprising the combination of a transformer having a primary and a secondary, rectifying means connected to said secondary to supply a direct current voltage, a capacitive load connected to said rectifying means to receive said direct current voltage, a saturable core impedance device having its main windings connected between an alternating current source and the transformer primary, a control winding for said saturable core impedance device, a magnetic amplifier of the self-saturating type having an output circuit connected to energize said control winding of said saturable core impedance device, a bias winding for said magnetic amplifier, circuit means connected to said bias winding to energize said bias Winding, said bias winding being wound to provide a saturating flux, a control winding for said magnetic amplifier wound to oppose said bias winding, and circuit means connecting said control winding with said primary of said transformer to be energized in dependence of a primary current surge to de-saturate the core of the magnetic amplifier.

5. Control apparatus for an electrostatic precipitator comprising, a transformer having a primary circuit and a secondary circuit, rectifiers connected to the transformer secondary circuit to supply the electrostatic precipitator with a direct current voltage, an alternating current circuit connected to energize said primary circuit of said transformer, a saturable core impedance device having a pair of main windings connected in series with each other and the transformer primary, a control winding for said saturable core impedance device, a magnetic amplifier of the self-saturating type having an output circuit connected to energize said control winding of said saturable core impedance device, a bias winding for said magnetic amplifier, circuit means connected to energize said bias winding, said bias winding being wound to provide a saturating flux driving said magnetic amplifier toward maximum output, and a control winding for said magnetic amplifier connected to said primary circuit of said transformer to be responsive to a system current surge, said control winding being wound in a sense to desaturate the core of the magnetic amplifier and drive said magnetic amplifier toward minimum output.

6. Electrical control apparatus comprising, the combination of a transformer having a primary circuit and a secondary circuit, rectifying means connectedto said secondary circuit. to supply a direct current voltage, an electrostatic precipitator connected to said rectifying means to receive said direct current voltage, an alternating 5 current circuit Connected to energize said primary circuit of said transformer, a first saturable core impedance device having its main windings connected in series with said transformer primary circuit, a control winding for said first saturable core impedance device, a second saturable core impedance device having an output circuit connected to energize said control winding of said first saturable core impedance device, a bias winding circuit for said second saturable core impedance device for driving said second saturable core impedance device toward maximum output, a control Winding circuit for a said second saturable core impedance device for driving said 6 second saturable core impedance device toward minimurri output, and circuit means responsive to transformer current surges for energizing said control winding of said second saturable core impedance device.

References Cited in the file of this patent UNITED STATES PATENTS 2,084,870 Schmidt June 22, 1937 2,549,782 Engelman Apr. 24, 1951 2,573,255 Forssell Oct. 30, 1951 2,617,973 Wolf J12, et a1 Nov. 11, 1952 

